scholarly journals Pumping Capacity of Pitched Blade Impellers in a Tall Vessel with a Draught Tube

10.14311/602 ◽  
2004 ◽  
Vol 44 (4) ◽  
Author(s):  
J. Brož ◽  
I. Fořt ◽  
R. Sperling ◽  
S. Jambere ◽  
M. Heiser ◽  
...  
Keyword(s):  
Flow Rate ◽  
Axial Component ◽  
Axial Distance ◽  
Turbulent Regime ◽  
Optimum Ratio ◽  
Mean Velocity ◽  
Power Number ◽  
Draught Tube ◽  
The Mean ◽  
The Absolute

A study was made of the pumping capacity of pitched blade impellers (two, three, four, five and six blade pitched blade impellers with pitch angles α = 35° and 45°) coaxially located in a cylindrical pilot plant vessel with cylindrical draught tube provided with a standard dished bottom. The draught tube was equipped with four equally spaced radial baffles above the impeller pumping liquid upwards towards the liquid surface. In all investigated cases the liquid aspect ratio H/T = 1.2 - 1.5, the draught tube / vessel diameter ratios DT /T = 0.2 and 0.4 and the impeller / draught tube diameter ratio D/DT = 0.875. The pumping capacity of the impeller was calculated from the radial profile of the axial component of the mean velocity in the draught tube below the impeller at such an axial distance from the impeller that the rotor does not affect the vorticity of the flow. The mean velocity was measured using a laser Doppler anemometer with forward scatter mode in a transparent draught tube and a transparent vessel of diameter T = 400 mm. Two series of experiments were performed, both of them under a turbulent regime of flow of the agitated liquid. First, the optimum height of the dished bottom was sought, and then the dependences of the dimensionless flow rate criterion and the impeller power number on the number of impeller blades were determined for both pitch angles tested under conditions of optimum ratio HT /DT. It follows from the results of the experiments that the optimum ratio HT /DT = 0.25 when the cross sectional areas of the horizontal flow around the bottom and the vertical inflow to the draught tube are the same. For all the tested pitched blade impellers the impeller power number when α = 45° exceeds the value of this quantity when pitch angle α  =   35°, while the flow rate number when α = 35° exceeds this quantity when α = 45°. On the other hand, the absolute values of the impeller power number when the draught tube was introduced correspond fairly well to the dimensionless impeller power input measured in a system without a draught tube. However, the absolute values of the flow rate number found in the former system are significantly lower than the dimensionless impeller pumping capacity determined in the latter system. The hydraulic efficiency of pitched blade impellers N3Qp/Po for the investigated geometry of the agitated systems does not depend on the number of impeller blades, but it is significantly lower than the quantity determined in an agitated system with a dished bottom but without the draught tube.

scholarly journals Effect of the Flame Dome Depth and Improvement of the Pressure Loss in the Dump Diffuser

1998 ◽  
Author(s):  
Shinji Honami ◽  
Wataru Tsuboi ◽  
Takaaki Shizawa
Keyword(s):  
Velocity Profile ◽  
Reynolds Stress ◽  
Flow Rate ◽  
Pressure Loss ◽  
Total Pressure ◽  
Flow Behavior ◽  
Sudden Expansion ◽  
Mean Velocity ◽  
The Mean ◽  
Stress Profiles

This paper presents the effect of flame dome depth on the total pressure performance and flow behavior in a sudden expansion region of the combustor diffuser without flow entering the dome head. The mean velocity and turbulent Reynolds stress profiles in the sudden expansion region were measured by a Laser Doppler Velocitmetry (LDV) system. The experiments show that total pressure loss is increased, when flame dome depth is increased. Installation of an inclined combuster wall in the sudden expansion region is suggested from the viewpoint of a control of the reattaching flow. The inclined combustor wall is found to be effective in improvement of the diffuser performance. Better characteristics of the flow rate distribution into the branched channels are obtained in the inclined wall configuration, even if the distorted velocity profile is provided at the diffuser inlet.

scholarly journals Unsteady low Reynolds number flow in a heated tube of slowly varying section

1988 ◽  
Vol 30 (2) ◽  
pp. 179-202 ◽  
Author(s):  
A. R. Bestman
Keyword(s):  
Fluid Motion ◽  
The Body ◽  
Axial Component ◽  
Axial Distance ◽  
Mean Flow ◽  
Steady Streaming ◽  
Reynolds Number Flow ◽  
Number Flow ◽  
The Mean ◽  
Oscillatory Pressure

AbstractFluid motion established by an oscillatory pressure gradient superimposed on a mean, in a tube of slowly varying section, is studied when the temperature of the tube wall varies with axial distance. Particular attention is focussed on the mean flow and steady streaming components of the oscillatory flow of higher approximation. For the velocity components, the axial component takes the pride of place, since this component is responsible for convection of nutrients to various parts of the body of a mammal in systematic circulation. A salient point in the paper concerns consequences of free convection currents at a constriction (stenosis).

Experimental Study of the Counter Dual-Swirl Air Blast Atomizer

2011 ◽  
Vol 130-134 ◽  
pp. 637-640
Author(s):  
Na Zhao ◽  
Yong Gang Yu ◽  
Qi Zhang
Keyword(s):  
Radial Direction ◽  
Radial Distance ◽  
Axial Distance ◽  
Exit Plane ◽  
Liquid Propellant ◽  
Mean Velocity ◽  
Air Blast ◽  
Circumferential Distribution ◽  
Center Axis ◽  
The Mean

With the Phase Doppler Analyzer (PDA), the distribution characteristics of the liquid propellant simulated media produced by the designed counter dual-swirl air blast atomizer are studied. The results indicate that, the maximum axial mean velocity decreases with the increase of the axial distance away from the swirl exit plane, but the uniformity of the distribution along the radial direction are better and the differences among the degree axes decay. The circumferential distribution of the droplets’ diameter is uneven. The uniformity of the droplets’ diameter decreases after increases along with the radial direction. The mean diameters of the droplets increase first, and then decrease with the increase of the radial distance away from the center axis. The distribution of the droplets along the radial direction is better as the spray evolves to downstream.

Fractal Orifices for Flowmetering

2012 ◽  
Author(s):  
Franck C. G. A. Nicolleau ◽  
Stephen B. M. Beck ◽  
Andrzej F. Nowakowski
Keyword(s):  
Wind Tunnel ◽  
Flow Rate ◽  
Velocity Profiles ◽  
Symmetric Design ◽  
Flow Properties ◽  
Mean Velocity ◽  
Fractal Pattern ◽  
The Mean

In this article we study the return to axi-symmetry for a flow generated after fractal plates in a circular wind tunnel. We consider two sets of plates: one orifice-like and one perforated-like. The mean velocity profiles are presented at different distances from the plate and we study the convergence of a flow rate based on these profiles. The return to axi-symmetry depends on how far was the original plate from an axi-symmetric design. It also depends on the level of iteration of the fractal pattern. In line with results for other flow properties [1, 2] It seems that there is not much to be gained by manufacturing fractal plates with more than three iteration levels.

Flow structure of the free round turbulent jet in the initial region

1979 ◽  
Vol 90 (3) ◽  
pp. 531-539 ◽  
Author(s):  
L. Bogusławski ◽  
Cz. O. Popiel
Keyword(s):  
Kinetic Energy ◽  
Turbulent Shear ◽  
Axial Distance ◽  
Initial Region ◽  
Mean Velocity ◽  
The Core ◽  
Turbulent Shear Stress ◽  
Air Jet ◽  
The Mean ◽  
Good Agreement

This note presents measurements of radial and axial distributions of mean velocity, turbulent intensities and kinetic energy as well as radial distributions of the turbulent shear stress in the initial region of a turbulent air jet issuing from a long round pipe into still air. The pipe flow is transformed relatively smoothly into a jet flow. In the core subregion the mean centre-line velocity decreases slightly. The highest turbulence occurs at an axial distance of about 6d and radius of (0·7 to 0·8)d. On the axis the highest turbulent kinetic energy appears at a distance of (7·5 to 8·5)d. Normalized distributions of the turbulent quantities are in good agreement with known data on the developed region of jets issuing from short nozzles.

Analysis of Transitional and Fully Turbulent Plane Couette Flow

1983 ◽  
Vol 105 (3) ◽  
pp. 364-368 ◽  
Author(s):  
J. R. Missimer ◽  
L. C. Thomas
Keyword(s):  
Couette Flow ◽  
Flow Analysis ◽  
Wall Region ◽  
Turbulent Regime ◽  
Plane Couette Flow ◽  
Burst Frequency ◽  
Mean Velocity ◽  
The Mean ◽  
Turbulent Plane ◽  
Turbulent Burst

The two-dimensional, incompressible, fully-developed, turbulent plane Couette flow is a limiting case of circular Couette flow. As such, plane Couette flow analyses have been used in lubrication theory to analyze the lubrication flow in an unloaded journal bearings. A weakness of existing analyses, other than the turbulent burst analysis, is that they are not capable of characterizing the transitional turbulent regime. The objective of the proposed paper is to develop a model of the turbulent burst phenomenon for momentum in transitional turbulent and fully turbulent plane Couette flow. Model closure is obtained by specification of the mean turbulent burst frequency and, for moderate to high Reynolds numbers, by interfacing with classical eddy diffusivity models for the turbulent core. The analysis is shown to produce predictions for the mean velocity profile and friction factor that are in good agreement with published experimental data for transitional turbulent and fully turbulent flow. This approach to modeling the wall region involves a minimum level of empiricism and provides a fundamental basis for generalization. The use of the present analysis extends the applicability of plane Couette flow analysis in lubrication problems to the transitional turbulent regime.

scholarly journals A study on the derivation of a mean velocity formula from Chiu's velocity formula and bottom shear stress

2011 ◽  
Vol 8 (4) ◽  
pp. 6419-6442 ◽  
Author(s):  
T. H. Choo ◽  
I. J. Jeong ◽  
S. K. Chae ◽  
H. C. Yoon ◽  
H. S. Son
Keyword(s):  
Shear Stress ◽  
Flow Rate ◽  
Estimation Method ◽  
Maximum Velocity ◽  
Mean Velocity ◽  
River Bed ◽  
The Mean ◽  
Bed Slope ◽  
Discharge Estimation ◽  
Discrepancy Ratio

Abstract. This study proposed a new discharge estimation method using a mean velocity formula derived from Chiu's 2D velocity formula of probabilistic entropy concept and the river bed shear stress of channel. In particular, we could calculate the mean velocity, which is hardly measurable in flooding natural rivers, in consideration of several factors reflecting basic hydraulic characteristics such as river bed slope, wetted perimeter, width, and water level that are easily obtainable from rivers. In order to test the proposed method, we used highly reliable flow rate data measured in the field and published in SCI theses, estimated entropy M from the results of the mean velocity formula and, at the same time, calculated the maximum velocity. In particular, we obtained phi(M) expressing the overall equilibrium state of river through regression analysis between the maximum velocity and the mean velocity, and estimated the flow rate from the newly proposed mean velocity formula. The relation between estimated and measured discharge was analyzed through the discrepancy ratio, and the result showed that the estimate value was quite close to the measured data.

scholarly journals Effect of turbulent fluctuations on the drag and lift forces on a towed sphere and its boundary layer

2013 ◽  
Vol 721 ◽  
pp. 155-179 ◽  
Author(s):  
Holger Homann ◽  
Jérémie Bec ◽  
Rainer Grauer
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Spherical Particle ◽  
Drag Force ◽  
Turbulent Regime ◽  
Mean Velocity ◽  
Turbulent Fluctuations ◽  
The Mean ◽  
Lift Forces ◽  
Drag And Lift

AbstractThe impact of turbulent fluctuations on the forces exerted by a fluid on a towed spherical particle is investigated by means of high-resolution direct numerical simulations. The measurements are carried out using a novel scheme to integrate the two-way coupling between the particle and the incompressible surrounding fluid flow maintained in a high-Reynolds-number turbulent regime. The main idea consists of combining a Fourier pseudo-spectral method for the fluid with an immersed-boundary technique to impose the no-slip boundary condition on the surface of the particle. This scheme is shown to converge as the power $3/ 2$ of the spatial resolution. This behaviour is explained by the ${L}_{2} $ convergence of the Fourier representation of a velocity field displaying discontinuities of its derivative. Benchmarking of the code is performed by measuring the drag and lift coefficients and the torque-free rotation rate of a spherical particle in various configurations of an upstream-laminar carrier flow. Such studies show a good agreement with experimental and numerical measurements from other groups. A study of the turbulent wake downstream of the sphere is also reported. The mean velocity deficit is shown to behave as the inverse of the distance from the particle, as predicted from classical similarity analysis. This law is reinterpreted in terms of the principle of ‘permanence of large eddies’ that relates infrared asymptotic self-similarity to the law of decay of energy in homogeneous turbulence. The developed method is then used to attack the problem of an upstream flow that is in a developed turbulent regime. It is shown that the average drag force increases as a function of the turbulent intensity and the particle Reynolds number. This increase is significantly larger than predicted by standard drag correlations based on laminar upstream flows. It is found that the relevant parameter is the ratio of the viscous boundary layer thickness to the dissipation scale of the ambient turbulent flow. The drag enhancement can be motivated by the modification of the mean velocity and pressure profile around the sphere by small-scale turbulent fluctuations. It is demonstrated that the variance of the drag force fluctuations can be modelled by means of standard drag correlations. Temporal correlations of the drag and lift forces are also presented.

scholarly journals The Role of Forcing and Eddy Viscosity Variation on the Log-Layer Mismatch Observed in Wall-Modeled Large-Eddy Simulations

2018 ◽  
Vol 141 (5) ◽  
Author(s):  
Rey DeLeon ◽  
Inanc Senocak
Keyword(s):  
Flow Rate ◽  
Eddy Viscosity ◽  
Degree Of Freedom ◽  
Channel Flows ◽  
Momentum Balance ◽  
Mean Velocity ◽  
Turbulent Channel Flows ◽  
The Mean ◽  
Viscosity Variation

We investigate the role of eddy viscosity variation and the effect of zonal enforcement of the mass flow rate on the log-layer mismatch problem observed in turbulent channel flows. An analysis of the mean momentum balance shows that it lacks a degree-of-freedom (DOF) when eddy viscosity is large, and the mean velocity conforms to an incorrect profile. Zonal enforcement of the target flow rate introduces an additional degree-of-freedom to the mean momentum balance, similar to an external stochastic forcing term, leading to a significant reduction in the log-layer mismatch. We simulate turbulent channel flows at friction Reynolds numbers of 2000 and 5200 on coarse meshes that do not resolve the viscous sublayer. The second-order turbulence statistics agree well with the direct numerical simulation benchmark data when results are normalized by the velocity scale extracted from the filtered velocity field. Zonal enforcement of the flow rate also led to significant improvements in skin friction coefficients.

scholarly journals Shear dispersion and residence time for laminar flow in capillary tubes

1984 ◽  
Vol 142 ◽  
pp. 289-308 ◽  
Author(s):  
J. E. Houseworth
Keyword(s):  
Residence Time ◽  
Molecular Diffusion ◽  
Capillary Tube ◽  
Point Sources ◽  
Capillary Wall ◽  
Axial Position ◽  
Axial Distance ◽  
Mean Velocity ◽  
Tube Cross Section ◽  
The Mean

The behaviour of passive tracer particles in capillary Poiseuille flow is investigated with regard to the residence time in short axial sections of length z, in which z/a < Va/D, where a is the capillary radius, V is the mean velocity and D the coefficient of molecular diffusion. While methods exist for calculating moments of the cross-sectionally averaged axial concentration distribution as a function of time (e.g. Smith 1982b), much less is known about the distribution of residence time as a function of axial distance. An approximate theoretical solution for point sources in high-Péclet-number flows reveals that the mean residence time 〈t(z)〉, which is asymptotic to z/V0 near the source, will then rise faster than z/V0 before converging to z/V for large z, provided the source is not at the capillary wall. V0 is the advective velocity at the point of release. The variance 〈t2(z)〉 is found to increase initially in proportion to z3 provided the source is not at the capillary wall or on the axis. A Monte Carlo method based on the solution to the diffusion equation in the capillary-tube cross-section is developed to compute particle trajectories which are used to analyse both axial and residence-time distributions. The residence-time distribution is found to display significant changes in character as a function of axial position, for both point sources and a uniform flux of particles along the tube.

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